st: tabulation of means, by group

Hello,
In the following simulated data, I'd like to create a table of mean
age (row header) for:
each of 3 income levels (with income level the column sub-header)
within each of 2 groups (with group the column main header)
So that:
from left to right in the data area would groups 1, 2, and 3,
within each group, from left to right would be income categories
And in each cell the mean age.